The problem is that I understand it all too well. Your easily exploited system isn't any better than what we have now, and, in fact, could be worse. I mean, it's not like anyone's going to roll up a bard, sorc or warlock with max charisma, right?
See? As I said, you don't understand the (suggested) system you are commenting on.
You made your mental imagine of how it would work, automatically assumed the least charitable scenario possible and ran away with it.
No one AT ANY POINT implied that JUST having high charisma would be enough to get a maximized discount.
A higher starting charisma would presumedly net to the player few additional percentage points, as a baseline to build over with reputation and accomplishments (i.e. doing the merchant a favor with a quest, etc).
Or maybe charisma may just net a greater gain of reputation/attitude points over time (i.e. every reputation point would be multiplied for a factor derived by your charisma. Like 1 reputation point at 10 CHA would become 1.8 reputation points at CHA 18 and so on).
But the funniest thing is that even assuming the worst case scenario, as you already did, you'd be WRONG anyway, because even a system where prices were fixed according to a character's charisma and that would be the end of it, would STILL be an improvement in stability and usability over the current one where prices fluctuate wildly in the most gimmicky way, and the only pre-requirement to get maxed reputation is gifting some pocket change to the merchant upfront, turning him instantly in your "best friend for life".
And none of this addresses the issue of having to do the little inventory dance between characters to maximize profits, anyway.
